Jar Launcher.app : where is it supposed to be located at

The Apple supplied java implementation comes installed with Mac OS 10.5 and 10.6 and .jar files are associated with the jar launcher application. As long as the java application starts right into a swing interface it should open without any problems.

On Mac OS 10.7 Lion however the java runtime is not installed by default and users trying to launch .jar files will be greeted with a dialog asking them to install java to continue (which requires admin privileges).

Officially the apple supplied java runtime is depreciated so you can't count on it working in any future version of mac os x

The problem is that you need to specify the class paths with the cp option to java and the library paths with the D option. The Minecraft launcher under /Applications handles this if you have a default install. If you want to run the default configuration from the commandline, just run something like the following with the memory values of your choosing:

java -Xmx2048M -Xms512M -jar \
/Applications/Minecraft.app/Contents/Resources/Java/MinecraftLauncher.jar

Here's an example of how I run Minecraft from the command-line for ad-hoc mode. I put the following in a script, name it and run it by name:

MCHOME="$HOME/Library/Application Support/minecraft/bin"
CP="$MCHOME/minecraft.jar:$MCHOME/lwjgl.jar:$MCHOME/lwjgl_util.jar:$MCHOME/jinput.jar"

java -Xmx2048M -Xms512M -cp "$CP" \
    -Djava.library.path="$MCHOME/natives" \
    net.minecraft.client.Minecraft